The Limbic System and the Reticular Formation

The limbic system and reticular formation are networks of neurons that function together even though they are widely separated.

The limbic system is the “emotional brain” made of deep gray matter structures linked together by the fornix. The fiber tracts have the appearance of oval fibers and looks like the corpus callosum but it’s not the same. The limbic system also includes certain structures of the diencephalon: the anterior thalamus and hypothalamus.

The hypothalamus in the middle of all this stuff has a direct between fearful stuff, memories and the autonomic nervous system. It’s a very strong anatomical connection.

The amygdala (fear and its sympathetic response) and hippocampus (form and retrieve memories) reside very close together.

The Reward Circuit

This is called the reward circuit because when studies were done with rats and were provided with pleasure, they would actually neglect their babies to the point of death. We are hardwired for fear and pleasure.

The reward circuit includes the prefrontal cortex which includes judgments, habits, and behavior.

Nucleus accumbens (physically deep in the frontal lobe) and Ventral tegmental area (physically part of the midbrain) both release and mediate the neurotransmitter, dopamine, which specifically produces and mediates sensations of pleasure and relaxation.

Because the limbic system output passes through the hypothalamus and reticular formation, it in turn controls visceral responses. Therefore severe emotional stress can easily lead to visceral disorders.

The Reticular Formation

Runs through the central core of the brainstem with connections throughout cerebral hemispheres. It is made up of ascending and descending fibers. It plays a big role in filtering incoming stimuli to discriminate irrelevant background stimuli. The Reticular Activating System (RAS) is made up of the reticular formation and its widespread connections. It maintains consciousness and alertness and functions during sleep and arousal from sleep.

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